2011年3月14日月曜日

After the earthquake

We design our buildings to deflect about one two-hundredth of their height in an earthquake. Although I am used to that on paper it was still amazing looking out from our office window along Roppongi-doori during the event on Friday to see 10-15 storey buildings swaying like trees. They looked just like the computer models we make for dynamic analyses.

A once in a lifetime view! My only mistake was not having a movie camera to hand.

Tokyo got away with limited structural damage. My condominium was left with some supicious diagonal shear cracks though. It's difficult to tell whether they are in zatsukabe or main walls. The shaking was 5+ on the scale 1-7, so buildings should still be within their elastic range.

Walking around Tokyo on Saturday I found that the same textbook cracking had occurred in one of the Imperial Palace outbuildings. This is probably of traditional wall construction so resistance is limited, but it does indicate that the shaking was just short of causing some major damage.

Some stores seem to be running out of supplies as the distribution networks are disrupted. We have power cuts planned from today in the areas surrounding Tokyo. This is one of the convenience stores just along from Ark Hills.

In general though the preparedness is impressive. It was bad luck that the particular circumstances of this earthquake caused a tsunami just too large for the defences to cope with. Probably well over a one in two hundered year event. My suggestion going forward is not to allow any timber buildings in Sanriku coastal towns, and also to provide refuge towers to hold four or five people at least 15m above the ground in each building.